(1) Technical Field
The present invention relates to techniques detecting concentrations of carbon monoxide. More specifically, the present invention relates to detecting and removing carbon monoxide in a hydrogen-based gas stream.
(2) Discussion
There are many examples where detection and quantification of carbon monoxide (CO) in hydrogen streams is necessary. Perhaps the most urgent application, however, is for the emerging fuel cell vehicle. The current strategy by automobile manufacturers developing fuel cell cars is to produce hydrogen gas onboard the vehicle via the reformation of either methanol or gasoline. In both cases, the reformation process produces a fuel cell feed stream containing hydrogen, but also carbon dioxide (CO2), water and small amounts of CO. The CO constituent has the effect of positioning the fuel cell at levels as low as 25 ppm. Therefore a method that allows for the monitoring and detection of CO at levels of greater than or equal to 25 ppm is desired.
Presently, the only reliable technique for sensing CO in hydrogen-based gas streams is by infrared absorption spectroscopy. However, to resolve species at very low levels, the intrinsic drift of the instrument and the interference from other species present in large concentrations, such as CO2 (at 18% by volume) and water (at 99% relative humidity) must be eliminated or compensated for during the measurement. While the infrared approach is viable, it does not represent a low-cost solution compatible with today's vehicle sensors or other commercial applications where such sensors would be useful.
Other sensors based on electrochemical approaches, while lower in cost, demonstrate similar interference problems with both hydrogen and water in the process gas stream. Since the hydrogen content in the target process stream is near 50% by value, with a relative humidity of 90-99%, detection of low levels of CO is not possible. At present, most fuel cells have attempted to address the problems associated with CO presence in the cell by designing the anode of the cell to avoid the effects of CO. Strategies include using high concentration of Platinum (≧1.0 mg/cm2) or CO insensitive alloys of Platinum (e.g., Pt/Ru) in a membrane electron assembly forming part of the fuel cell.
Many other sensors that measure CO in air have been developed based on biomimetic, electrochemical, and resistive-based elements. They represent a low-cost approach for home or laboratory monitoring where the hydrogen concentration in the target gas is minimal. Each of these approaches, however, has a strong interference from hydrogen and is incapable of making accurate CO determinations when this interfering species is present in abundance.
Accordingly, there exists a need in the art for a reliable, reusable and low-cost system for detecting CO in desired gas streams. There is also a need for a system that can meet the aforementioned requirements while having the relatively low response time and freedom from interference when performing CO measurements.